SmartFin

FIRE number and years to reach it

smartfin_calculate_fire_number

Read-onlyIdempotent

Works the way SmartFin's FIRE calculator does. The FIRE number today is yearly expenses divided by a withdrawal-rate assumption. Each year savings grow at an assumed return with the yearly savings added, while expenses (and so the FIRE number) rise with inflation; FIRE is the first year savings reach that year's FIRE number, searched up to 60 years. Also gives the savings rate and, with a traditional retirement age, the Coast FIRE number. Use for early retirement / FIRE questions: "how much do I need to retire", "when can I retire", "what's my coast FIRE number". Do not use to test how long an existing balance lasts (use smartfin_calculate_retirement_withdrawal). Returns and inflation are assumptions; excludes taxes.

Input Schema

TableJSON Schema

Name	Required	Description
`currency`	No	Currency symbol for the amounts in the summary only; amounts are never converted. The link opens the page in US dollars, and how_to says to pick the currency there. Default USD
`current_age`	No	For the age at FIRE and Coast FIRE. Default 30
`inflation_pct`	No	Yearly inflation in %, applied to expenses. Default 3
`annual_savings`	No	Added each year, in the currency chosen (12 x a monthly amount). Default 0
`retirement_age`	No	Optional: a traditional retirement age, for the Coast FIRE number
`annual_expenses`	Yes	Yearly spending today, in the currency chosen
`current_savings`	No	Invested today, in the currency chosen. Default 0
`expected_return_pct`	No	Assumed yearly return in %. Default 7
`withdrawal_rate_pct`	No	Withdrawal-rate assumption in %. Default 4

Output Schema

TableJSON Schema

Name	Required	Description
`cite`	Yes	How to credit this result
`data`	Yes
`next`	Yes	Suggested follow-up calls
`links`	Yes
`how_to`	Yes	Steps for the user to see or redo this on smartfin.fyi
`source`	Yes
`summary`	Yes	Plain-language result the assistant can quote

Schema Changelog

Changes observed during successful MCP inspections.

Changed4 schema fields changedOct 18, 2026

changedInput schema / properties / annual_expenses / description

Previous value: -"Yearly spending today, in dollars"New value: +"Yearly spending today, in the currency chosen"

changedInput schema / properties / annual_savings / description

Previous value: -"Added each year, in dollars (12 x a monthly amount). Default 0"New value: +"Added each year, in the currency chosen (12 x a monthly amount). Default 0"

addedInput schema / properties / currency

Added value: +{
+  "description": "Currency symbol for the amounts in the summary only; amounts are never converted. The link opens the page in US dollars, and how_to says to pick the currency there. Default USD",
+  "enum": [
+    "USD",
+    "EUR",
+    "GBP",
+    "CHF",
+    "AUD",
+    "CAD",
+    "SGD",
+    "HKD",
+    "INR",
+    "JPY"
+  ],
+  "type": "string"
+}

changedInput schema / properties / current_savings / description

Previous value: -"Invested today, in dollars. Default 0"New value: +"Invested today, in the currency chosen. Default 0"

Changed1 schema field changedOct 6, 2026

changedInput schema / properties / withdrawal_rate_pct / description

Previous value: -"Safe withdrawal rate in %. Default 4"New value: +"Withdrawal-rate assumption in %. Default 4"

Changed1 schema field changedSep 29, 2026

addedOutput schema / properties / links / properties / page

Added value: +{
+  "description": "SmartFin's page for this stock, when it has one",
+  "type": "string"
+}

First observedSep 29, 2026

TDQS

A4.6/5.0

Behavior5/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations cover the safety profile (readOnly, idempotent, closed-world, non-destructive), and the description adds substantive behavior beyond them: the FIRE search is capped at 60 years, returns and inflation are user assumptions rather than facts, taxes are excluded, and the coast FIRE number only appears when a traditional retirement age is supplied. These are real computational limits an agent should know before answering.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

Front-loaded with the mechanism, then usage, then exclusion, then caveats, with no filler sentences. The algorithm walkthrough is somewhat long, but each clause carries information needed to interpret the result.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness5/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a nine-parameter calculation tool with an output schema and full annotation coverage, the description supplies the model, the search bound, the optional coast FIRE branch, the exclusion, and the assumption caveats. Nothing material is missing for correct invocation or interpretation.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100%, so every parameter (currency, inflation, savings, withdrawal rate, retirement age) is already documented in the schema, and the description mostly restates that the withdrawal rate and return are assumptions. It adds no syntax or unit detail beyond the schema, so the baseline 3 applies.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific computation (the FIRE number and the year it is reached) and explains the underlying model: expenses divided by a withdrawal rate, savings growth, inflation on expenses. It also names the sibling it is not (smartfin_calculate_retirement_withdrawal), so an agent can route correctly without opening the schema.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines5/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

Explicit 'Use for early retirement / FIRE questions' with concrete user phrasings ('how much do I need to retire', 'when can I retire', 'what's my coast FIRE number'), plus a hard exclusion: 'Do not use to test how long an existing balance lasts (use smartfin_calculate_retirement_withdrawal).' Both the when and the when-not are present with the alternative named.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

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